The present invention relates generally to spacecraft orbit maintenance systems, and more particularly, to an automated spacecraft orbit compensation system designed for a geosynchronous (GEO) satellite.
The assignee of the present invention manufactures and deploys spacecraft that orbit the Earth. Most stationkeeping is performed with a human operator which results, in substantial manpower costs when the stationkeeping is performed frequently. U.S. Pat. Nos. 5,528,502 and 5,687,084 entitled "Satellite Orbit Maintenance System" disclose an automated orbit-maintenance system which is located on-board a spacecraft.
More particularly, U.S. Pat. Nos. 5,528,502 and 5,687,084 entitled "Satellite Orbit Maintenance System" disclose techniques for maintaining a satellite in an assigned Low Earth Orbit (LEO) without control or intervention from the ground. Autonomously obtained navigational data provide a measurement of the actual orbit in which the satellite is traveling. So long as the measured orbit conforms to a desired orbit to within a preselected tolerance, periodic corrections of equal magnitude are made to the satellite's velocity, based on a prediction of the effect of atmospheric drag on the orbit.
Measurement of the orbit is made by observation of the time that the satellite passes a reference point in the orbit, such as by crossing the ascending node. If the measured orbit departs from the desired orbit by more than the preselected tolerance a velocity correction of a magnitude different from the one based on prediction is applied to the satellite.
For a decaying orbit, the magnitude of the velocity correction is increased above the correction value based on prediction. For a rising orbit, the magnitude of the velocity correction is decreased below the value based on prediction. It may be reduced to zero in low earth orbit (LEO) if the prediction shows that the atmospheric drag will bring the measured orbit back within the preselected tolerance range.
Accordingly, it is an objective of the present invention to provide for an improved automated spacecraft orbit compensation system that is not located on-board a spacecraft, and does not rely on natural perturbations to bring the measured orbit back within a preselected tolerance range. The present invention is also geared toward GEO rather than LEO satellites.